The invention relates to a device for isolating an electric circuit, especially for high current intensities.
Switches, or in the most general of meanings, devices are needed for the most diverse applications, which will quickly and safely, in irreversible manner, isolate an electrical circuit, especially in case of injury or other emergencies, in order to prevent damage to technical equipment or endangerment of human beings. Such devices are especially required when high current intensities are present in technical equipment,.for example in energy distribution networks or in automotive engineering. Such devices for isolating an electric circuit must meet high safety requirements; in particular, the electric circuit must be isolated sufficiently quickly and securely, in irreversible fashion, without possibility of causing injury to technical equipment or human beings by the switching process itself In addition, such devices must be highly maintenance free, and be able to function reliably, even after long periods of inactivity, for example, even after up to 20 years.
In automotive engineering, it is necessary or desirable, in case of accident, to definitely and irreversibly separate, in the shortest possible time, the battery from the wiring of the vehicle. In this fashion it is possible to avoid sources of ignition formed by sparks and plasma, which are created when cable isolations are scraped off during an accident due to sheet metal penetration from the car or loose cable ends hitting against each other or against sheet metal parts, and which may ignite escaping gasoline or cause an explosion of ignitable gasoline-air mixtures developing after an accident.
An electric safety switch is known from DE 297 00 594 U1 to realize a device for isolation of an electric circuit in which high intensity current flows, in regard to which a conductor, located in a housing, is isolated by means of a pyrotechnically accelerated, electrically isolating separation body.
In its original position, the separation body is located at a certain distance from the conductor element to be severed and is accelerated in the direction toward the conductor element, following the triggering of a propellant charge provided in a combustion chamber, for example due to a signal which also serves for triggering an air bag.
As a result of an indentation in the otherwise relatively large cross-section of the conductor element, the conductor element or this separation area breaks very quickly. Underneath the conductor element to be severed, space is provided into which are bent the conductor ends to be severed, and which also accepts the separation body. Thus, with this device, the conductor ends are not torn off or ejected in uncontrolled fashion. However, if with this type of a device, a high intensity current flows within the conductor element, an electric arc is formed as soon as a cut-off occurs in the conductor element, so that initially the flow of current continues at practically full intensity.
The electric arc is then, however, extinguished extremely quickly via the electrically isolating separation element. While this results in achieving a quick, irreversible shut-off of the current flowing from the battery to the consumers or of a short-circuit current, very high tension peaks are created by self-induction, due to the always existing inductivities in the load of the circuit, as a result of which there is the risk of causing irreversible damage to connected instruments and isolations.
In addition, a pyro-technical separation device is known from DE 44 38 157 C1, which likewise operates according to the same principle. Here also, an isolating separation element is accelerated by means of a propellant charge and cuts-off an element to be severed. Toward that end, the separation element is preferably provided with a frontally formed concave recess, so that a circumferential cutting edge is formed in the marginal region. This device is to ensure safe and very quick separation of also heavier conductor elements with a relatively low force propellant charge. If such a separation device is employed as electrical switch, there again results the problem of high induction voltages due to the very rapid interruption of the flow of current.
Moreover, the known devices require, for adequate acceleration of the separation element, propellant charges which constitute a certain risk potential, despite a correspondingly designed massive housing. The known device must pass costly approval tests, which involves considerable expenditure in terms of time and finances.
Differently constructed devices for the isolation of power currents, as they are known from power engineering, are not being considered here, since they are constructed in relay fashion. and thus do not begin to achieve the specified reliability (to also function reliably after 20 years without single switching and without maintenance) given the mechanical and thermal/climatic environmental conditions which occur in a motor vehicle. Moreover, such devices are still too expensive by far and/or too heavy or too large for application in automotive engineering, even with corresponding simple design.
Starting from the initially mentioned state of the art, the invention is based on the object of creating a device for isolating an electric circuit, especially for high current intensities, which, on the one side, irreversibly isolates the circuit to be severed, safely and with sufficient speed, and which, on the other side, avoids damage to structural components located within the electric circuit by induced voltage peaks.
The invention solves said object with the characteristics of Patent Claim 1.
The invention initially proceeds from the knowledge that an acceptable compromise must found with respect to the speed of the process with which an interruption takes place of the current flowing in the electric circuit, which, on the one hand, assures quick enough interruption of the current in order to avoid danger to equipment and persons from the (perhaps unduly high) current, and, on the other hand, does not interrupt the current so quickly that there may be danger to equipment and persons from induced voltage peaks; in other words, quantity-wise, the changes in electricity di(t)/dt must not become too significant.
According to the invention, in contrast to the known devices, no separation element is employed which has already been accelerated to high speeds of 150 to 200 m/s for example prior to impact on the conductor element or the isolating area of the conductor element, which isolates the conductor element extremely rapidly and extinguishes the potentially developing electric arc. Instead, the isolating area is directly acted upon by a triggering pressure or via a driving surface impinging already in the original position on the isolating area. Needless to say, the driving surface in its original position can also be located at such short distance from the isolating area that upon impact, the latter has only a relatively low speed of several meters or several tenth of meters per second.
As a result, following the generation of the triggering pressure, the separating area is isolated with sufficient speed, but not so quickly that unacceptably high induction voltages develop. Since no acceleration path is needed for an isolation element that is to be accelerated, it is possible to realize extremely small construction sizes. Such devices can be attached, for example, directly to the battery clamp of a car battery.
According to the invention, in an alternative [solution] the entire conductor cross-section can be isolated in the isolating area by actuation of pressure on the isolating area.
In another alternative, it is possible to isolate only a portion of the conductor cross-section in the isolating area, with ability for the remaining portion to still maintain, for a predetermined period of time, consumer emergency functions, especially in automotive vehicles. To that end, the remaining conductor cross-section is dimensioned in such fashion that the current which flows over the conductor cross-section is sufficient in order to heat a cross-sectionally reduced isolating area according to a safety fuse and to then fully isolate. The conductor cross-section over the length of the isolating area, and the length of the isolating area, can be dimensioned in such manner that the resistance of the reduced isolating area suffices in order to reduce the current over the conductor element to such a low value that there is no possibility of endangering equipment and persons, and that, nevertheless, emergency supply of consumers with electricity can be maintained for the pre-determined period of time until melting of the isolating area takes place. Additionally, the material of the reduced isolating area can be selected in such manner that it takes on a pre-determined resistance value.
In the preferred embodiment of the invention a chamber is provided in the housing which is filled, after activation, at least in part with an activatable, thermal energy emitting and/or gas producing medium, preferably a pyrotechnical material or a gas with internal or chemical energy, whereby via activation of the medium the triggering pressure can be generated which acts directly or via the driving surface on the isolating area.
The isolating process, by selecting the appropriate pyrotechnical mixture, and the bum-up and/or the behaviorxe2x80x94supported by the appropriate design of the cross-section of the isolating areaxe2x80x94can thus be controlled in such manner that the cut-off of the current, including extinction of the developing (plasma) electric arc, which develops with high current intensities, takes place with such rapidity so that it is possible to xe2x80x9cuse upxe2x80x9d the otherwise destructively acting induction energy.
In another specific embodiment of the invention, an ignition- or igniter-piece may be provided for activation of the medium. As with known devices, this has the result that the medium is very quickly activated and the medium, in turn, very quickly develops the triggering pressure.
In another specific embodiment, a conductor is provided for activation of the medium which is heatable by electrical current or a conductor that can be brought to explosion by very high current intensity. In particular, with employment of only one heatable conductor, for example a glowing filament, one obtains the benefit of extremely simple construction and medium activation.
According to another specific embodiment of the invention, the activatable medium can be activated by means of a hot gas, which can be transmitted to the chamber, whereby the hot gas can preferably be transmitted from another device for isolating an electric circuit. In particular, this achieves that with an activation of a first device for isolating a first electric circuit, there inevitably also occurs activation of a second or of several additional devices for isolating a second or several additional electric circuits. It should be noted here that, of course, there may also be provided, in one common housing, several isolatable conductor elements with associated activatable means for isolating the respective conductor element.
According to the preferred specific embodiment of the invention, the activatable medium can be activated by thermal energy, which is emitted by the conductor element, in particular the isolating area, in the event that the temperature of the conductor element or the isolating area surpasses a pre-determined value, whereby the medium preferably maintains good thermal contact with the conductor element and/or the isolating area. Consequently, an activation of the device is also then assured if no activation device is provided that can be acted upon by means of a signal, for example in form of a glowing filament or an ignition- or igniter piece, or if an existing. actuatable activation device is non-functional or an actuating signal can no longer be generated.
In one specific embodiment of the invention, a pot-shaped driving surface is provided or a driving surface presenting a pot-shaped area, whereby the driving surface acts with the frontal surface of the outer wall upon the isolating area. The driving surface acts hereby as a punch. The isolating area is preferably designed in such manner that outside the area in which the driving surface acts with its frontal surface of the outer wall upon the isolating area, there is provided a weakening of the isolating area vis-a-vis the cross-section of the conductor element adjacent to the isolating area.
The punch-like driving surface presses or breaks out after an activation of the device either a partial piece of the isolating area which isolates the entire cross section of the isolating area or only an appropriate part. In case of the latter, the weakening of the isolating area preferably extends in form of a closed curve or a curve open only toward one side of the isolating area, so that either a perforation of the isolating area is xe2x80x9cpunched outxe2x80x9d or a recess which is open toward one side of the isolating area.
Of course, the breaking out of partial pieces of thusly shaped isolating areas cannot only be done with the utilization of a driving surface but also with direct pressure actuation on the isolating area.
In other instances, the isolating area can also be designed in such manner that an entire piece or several partial pieces are not broken out but that the isolating area is broken up in one or several specific areas, whereby in each case there is at least a reduction of the conductor crosssection. For breaking up, the isolating area can be designed so that it breaks along weaker lines in one area and that the partial areas are bent over like flaps.
In a further specific embodiment of the invention, the interior of the pot-shaped driving surface or the pot-shaped area is filled, at least in part, with a heat activatable medium which emits thermal energy and/or generates gas after its activation, said medium preferably constituting a pyrotechnical material or a gas with interior or chemical energy, whereby the medium is in good thermal contact with the conductor element and/or the isolating area.
In another specific embodiment, the isolating area consists, at least in part, of a material having in comparison with the other conductor element, poorer conductive properties. It is possible to thus achieve, on the one hand, that this area heats up more intensively compared with the other conductor. With respect to the specific embodiments in which automatic activation of the thermal energy and/or gas producing medium is desired, with unduly high flow, by means of the thermal energy generated in the conductor element and/or in the isolating area, it is possible to achieve same in that a medium can be employed having a relatively high activation temperature, but that nevertheless triggering of the device is desired with relatively low flow and/or low conductor temperatures. Furthermore, by using a material with poorer conducting qualities in the isolating area, it is possible to obtain the function of a safety fuse, in particular with respect to specific embodiments in which the conductor element is not totally interrupted after an activation.
In such cases the conductor cross-section which is still effective after an activation can consist, at least in part, of the material having poorer conductive qualities.
In another specific embodiment there is provided, at the pressure-actuatable surface of the isolating area, a flexible membrane which seals off the chamber or the interior of the pot-shaped driving surface. As is the case with a driving surface, this ensures that upon actuation of the isolating area by pressure, there is initially no development of minor perforations in the isolating area and reduction in pressure via these perforations, without producing the desired complete or partial isolation of the isolating area.
In another specific embodiment, the driving surface can consist of memorious material, whereby the driving surface, upon surpassing a threshold temperature (activation) moves to a latent shape which, in transverse direction relative to the conductor element, presents a larger expansion than the shape of the driving surface in the original position at a temperature which is lower than the threshold temperature, whereby the driving surface supports itself, relative to the housing, with one end on a stationary stop and thus, upon activation, acts upon the isolating area with pressure, isolating same, at least partially.
In the specific embodiments of the invention where at least a partial area of the isolating area can be broken out by pressure actuation, there is preferably provided in the housing a collecting space for accepting the broken out partial area. The collecting space ensures that after an activation of the device, equipment and persons are not put at risk from fragments of the isolating area.
The collecting space may be designed geometricallyxe2x80x94or means may be provided in the collecting spacexe2x80x94so that after the pressure-actuated break-out and push-in of the partial area into the collecting space, the partial area is fixed in a position remote from the remaining partial area or the isolated conductor element. This prevents another unintentional closing of the severed electric circuit by broken-out conductor pieces which are located loosely in the collecting space.
In the preferred specific embodiment, following the activation of the medium in the chamber of the housing or in the interior of the pot-shaped driving surface and after the breaking-out of at least a partial area of the isolating area, a gas flow is generated over the at least partially isolated isolating area. The gas flow, which is generated by the triggering pressure exercised on the isolating area, can cool, after the break-out of a partial piece or the isolation of the isolating area, a plasma which may be generated, in case of high flows, immediately after the isolation, whereby, it is possible to additionally attain a relatively slow current decrease during the xe2x80x9cswitch-offxe2x80x9d process and thus low induction voltages. On the other hand, the gas flow also serves for safely xe2x80x9cblowing outxe2x80x9d the plasma, if no isolating driving surface is employed.
In a specific embodiment according to the invention, the collecting space may have openings for the escape of the gas volume which is to be displaced from the collecting space and/or for the gas volume which is generated by the triggering pressure. Based on the dimensioning of the openings, it is possible to adjust the force of the gas flow over the isolating area in the desired fashion.